1.a
Changing Rank System (US, Germany, France, Japan, Italy, etc.)
This is changed while you are using the Online game.
Go to my records. On the page that shows your achievements you will see some flags of the different nations under your player icon. Select a different flag and it will change rank to be from that nation.

One more question - On the scenario list, I occasionally see some scenarios in green, why are they green?

A green highlighted scenario indicates one of two things:

1. Someone has entered a scenario to play and has no opponent. That person is waiting for anyone who would like to join that scenario with the hopes of playing.

2. DOW has technical issues with a scenario that has become stuck open on the server, even though there is no one actively seeking a game. In this case a technical error causes the game to indicate (green) even when no one is there. The only current remedy for DOW to clear this false open scenario is to shut down the server to reboot the program. They are reluctant to do this as it interrupts service for everyone when it is only a "cosmetic" issue. So until they have a real need to update software or otherwise make a change the "cosmetic" issue will probably remain. RZHEV is one of those scenarios currently stuck.

If you want to play a GREEN scenario just go ahead, but be warned that no one may join currently because they think no one is there. Just use the chat bar or INVITE button to make contact and you should be okay.